The present invention relates to a white laminated polyester film and a imaging medium (recording medium or printing medium), and more particularly, relates to a white laminated polyester film having excellent surface glossiness and a imaging medium using the same.
Recently, an ink jet printing system is rapidly applied to various types of facsimiles, printers and plotters because of many advantages of this printing system over the conventional art, such as low noise, capability of high-speed imaging, easy adaptability to full color printing and low cost.
On the other hand, by enhancement of printing speed and prevalence of full color printing requires further improvement in quality of the imaging sheets (recording sheets or printing sheets) and many studies on the imaging sheets have been made. For instance, the requirements for the hue b value and surface gloss of the imaging sheet have varied from the conventional standards for increasing clearness of the printed images, and similar review is being made on use of synthetic paper or plastic film as imaging sheet.
The plastic film used as imaging sheet is usually a white film containing a white pigment.
However, with such white films containing a white pigment, although it is possible to control the hue b value in a satisfactory way when the film is composed of a single layer, there are limitations on the improvement of surface gloss that can be attained by use of white pigments, thereby making it difficult to obtain a desired high-gloss film.
The imaging layer (recording layer or printing layer) of the imaging sheet applicable to the ink jet printing system is usually formed by applying on the base film a coating solution mainly composed of polyvinyl alcohol which is a water-soluble resin.
Incidentally, the binder resin of the imaging layer is mainly composed of a water-soluble resin, however, is unsatisfactory in its adhesiveness to the base polyester film, and it is hardly possible to obtain satisfactory adhesion between the imaging layer and polyester film even if a known easy-adhering resin layer is provided therebetween.
As a result of the present inventor's earnest studies to solve the above problems, it has been found that by laminating a layer of a different polyester on at least one side of the white polyester film, and further forming thereon an easy-adhering layer and a imaging layer, the thus obtained white polyester film is free of the above problems. The present invention has been attained on the basis of the above finding.